• Important to know PD of acyclovir.
  • Zidovudine, amphotericin and the azoles are small print, and the key points have been summarized below.
  1. DNA polymerase inhibitor
  1. It is a prodrug that requires activation by viral thymidine kinase before become active.
    • It then functions by inhibiting viral DNA polymerase, preventing replication of viral DNA.
    • Spectrum of activity as follows: HSV-1, HSV-2 and VZV. No in vivo activity against EBV/CMV and HHV-6.
    • Therefore, indications as follows:
      1. Herpes simplex encephalitis
      2. Neonatal HSV
      3. Serious HSV/VZV infections, especially in the immunocompromised
  2. Resistance is due to reduction in viral thymidine kinase or the alteration of DNA polymerase binding site. If there is a reduction in the viral thymidine kinase, then the virus will have cross resistance to valacyclovir, ganciclovir and famciclovir.
  1. PO or IV. Bioavailability is very low.
  1. Readily distributes into most tissues and body fluids, with CSF concentrations approximately 20-50%.
  1. Not metabolized – it is excreted unchanged in the urine.


  1. T ½ of 2.5 hours, which is prolonged in renal failure.
Adverse events  
Withdrawal syndrome  
Special notes